You can certainly keep the 3400G without the IGP graphics enabled and use a discrete card instead. Which card you can use will be limited by the motherboard and power supply you have. Also be aware the 3400G only supports PCIe gen 3.0 and all modern graphics cards are gen 4.0 so there will be some performance loss.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT